We propose to conduct a longitudinal study to investigate ways in which genes and environmental factors contribute to cognitive and adaptive aging, and how the relative influence of genes and environmental factors may change over time. We will study the now middle-aged subjects from the Vietnam Era Twin Registry who we have been studying for the past 12 years. We will study 360 pairs of twins at age 51 years and 360 pairs at age 56, for a total sample of 720 twin pairs (Our colleagues at the U. C. -Davis are concurrently submitting a grant application that parallels ours. In our application we are requesting funding to collect data from 360 pairs in our lab in Boston and in our colleagues' application, they are requesting funding to collect data from the other 360 pairs at their lab in Sacramento. The two applications comprise an integrated project.) Based on a broad, conceptual model of cognitive and adaptive aging, our Specific Aims are: 1) To characterize normative age-related changes in individual cognitive, health, and personality variables using the classical twin method (univariate approaches); 2) To explicate the bases of patterns of inter-relationships seen within the cognitive domain and between cognitive and non-cognitive variables using bivariate, multivariate, and longitudinal approaches; and 3) To characterize risk factors for change in cognitive and adaptive functioning during mid- and later-life using a co-twin control approach. We propose to address developmental issues by means of: 1) cross-sectional data from the twin cohorts; 2) cognitive and personality data collected previously from this sample; and 3) future longitudinal/cohort sequential data In contemporary data collection we will include genotyping for APOE, personality traits and characteristics that have implications for later life cognitive functioning and well-being (attachment, coping styles, positive and negative emotionality, constraint, resiliency), sensory functioning, and physical functioning. Cognitive assessment will consist of an extensive neuropsychological test battery with particular emphasis on working memory and frontal-executive function, episodic memory, and processing speed. This project will shed light on the dynamic interplay of biological and psychosocial environmental factors that create age-associated changes in health, cognition, and personality. Beginning the project in midlife is particularly advantageous for studying adult aging, enabling us to assess subjects who are in the "prime of life" at baseline, yet relatively close to the time when age-associated changes are likely to become more prominent.